Monoprolellant/hypergolic powered proportional actuator

ABSTRACT

Systems and methods involving monopropellant and hypergolic powered proportional actuators that may be used in applications such as robotics. A blowdown tank delivers fuel to a reaction site, produce gaseous products. Those gaseous products are transported to a pressure reservoir or directly to the actuator. The gaseous products are controllably introduced into the actuator to actuate a piston. The piston may be used to power a host of devices including robots.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to the fields ofmonopropellants, hypergolic bipropellants, robotic actuators, androbotic power sources. More particularly, it concerns the use of amonopropellant or hypergolic bipropellant to power a robotic actuator.Even more particularly, the liquid fuels are utilized to generategaseous products, which are in turn used to proportionally control theforce or motion of a gas actuator.

2. Description of Related Art

A major concern facing those who design and build untethered mobilerobots involves finding a suitable source of power and actuation forthose robots. Note that unlike an engine, an actuator is characterizedby controllable positive and negative power output across a bandwidththat typically spans from DC to several Hertz. Unlike tethered robots,untethered robots are not permanently connected to one or more powersources. Thus, untethered robots typically rely upon power that iscarried upon the robot itself. The power supply most often used foruntethered robots is battery power. Although battery power is effectivein its own rite, it suffers from significant shortcomings.

Specifically, electrochemical batteries contain insufficient massspecific energy density to perform human-scale work for extended periodsof time. For example, one of the more advanced current mobilerobots—Honda's P-3 Humanoid Robot—has an operation time of only 15-25minutes, depending on its workload. Operation times of this magnitude orsmaller are not uncommon and represent one major technological roadblockfor designing mobile robots that can operate remotely for extendedperiods of time. It should be noted that a trade-off generally existsbetween the mass-specific energy density and power density of currentelectrochemical battery technology. That is, batteries that providerelatively high energy densities typically suffer from relatively lowpower densities, and vice-versa. Therefore, though certain high energydensity batteries do exist, they are generally incapable of providingthe power required for human-scale mechanical tasks.

Electric motors are the most common type of actuator that would be usedwith batteries. For purposes of robotics, the peak mechanical poweroutput of a motor is in a high speed and low torque regime, whereasrobot motion is in a relatively low speed and high torque regime.Therefore, appropriate use of electric motors in robots generallyrequires a speed-reducing gearbox, which increases the size and weightof the actuation package.

An additional drawback to robotic actuation with electric motors is thefact that they consume electrical power in order to dissipate mechanicalpower. That is, robotic actuators must often absorb mechanical powerfrom a load (e.g., lowering a payload under the influence of gravity).Rather than absorb that energy, an electric motor requires electriccurrent for instantaneous control of torque, which in turn requireselectrical power to dissipate mechanical power. Electric motors aretherefore energetically expensive robotic actuators.

Hydraulic actuators can be used to transmit hydraulic power intomechanical power, but they require a source of hydraulic power.Hydraulic power must in turn be provided by a hydraulic pump, which istypically either electrically powered (i.e., battery powered) or fuelpowered (i.e., gasoline or diesel engine powered). These systems aretypically too heavy for human scale robots.

Internal combustion engines can also be used as a source of power formobile robots. Such an engine cannot be used directly, since the outputcannot be force or motion controlled over the bandwidths typicallyrequired of human-scale robots. An engine can, however, be utilized todrive a hydraulic or pneumatic pump or compressor to power afluid-powered system, or alternatively to drive a generator to providepower for an electrically powered system. The added complexity of suchsystems, however, degrades the overall system energy density.

In view of shortcomings such as those outlined above, it is apparentthat a better source of controllable power for use with untetheredmobile robots would be desirable. This disclosure demonstrates that abetter power and actuation source involves the use of monopropellants orhypergolic bipropellants. Although monopropellants (or hypergolicbipropellants) have been used as fuel-types in specialized applications,their potential has not been realized for use with untethered mobilerobots until this invention.

U.S. Pat. No. 4,825,819 involves a fluid-powered actuator with aslidable piston. This patent essentially describes the operation of abistable pilot-operated valve. Specifically, the valve draws from theprimary fluid stream of fuel and oxidizer (or monopropellant) to switcha primary stream valve into either an on or off position. The actuatoris therefore designed to move to one position or the other, and unlikethe actuator described in this application, cannot provide proportionalforce or motion control. In other words, no disclosure is present tosuggest how one can use monopropellants to continuously vary the outputof one or more robotic actuators.

U.S. Pat. No. 5,992,700 involves an infusion device including a pressurecontainment pouch. In certain embodiments of the disclosure, gas isgenerated by drawing an aqueous solution of a peroxide or superoxideinto an absorbent tablet that contains an enzyme or catalyst whichpromotes the decomposition of the peroxide or superoxide todecomposition products including oxygen gas. Although useful forapplications such as medicine, this reference likewise does not discloseor suggest mechanisms whereby monopropellants may be used as a usefulpower source for untethered mobile robots.

U.S. Pat. No. 3,601,827 involves a self-contained underwater buoyancysystem including a fuel tank containing a monopropellant fuel and a gasgenerator assembly that has a main body portion housing a catalyst bedthat causes the monopropellant fuel to turn into a gas. The buoyancysystem allows users to control buoyancy so that, a load of 1,000 poundsmay be lifted at a depth of 150 feet. Although useful as applied toassisting underwater lifting, this reference does not disclose orsuggest principles necessary to implement monopropellant power suppliesin untethered mobile robots.

U.S. Pat. No. 5,932,940 involves a micro-gas turbine engine. Thedisclosure contemplates a wide range of propellant combinations,including monopropellants, such as hydrazine and hydrogen peroxide,which are preferably employed with the addition of a catalyst. Thisreference also does not disclose or suggest principles necessary toimplement monopropellant power supplies in untethered mobile robots.

U.S. Pat. No. 3,581,504 involves a gas generator including an inlet foradmitting a monopropellant. The disclosed gas generator provides apressure-amplifying staged expansion cycle wherein relatively lowpressure monopropellant is pumped by an impeller to a higher pressure.The monopropellant is then decomposed in the presence of a catalyst toproduce a higher pressure exhaust gas. The disclosure states that asuitable monopropellant is hydrogen peroxide. Although useful to assistin techniques for pressure amplification, this reference does notdisclose or suggest the applications discussed and claimed hereininvolving the use of monopropellants as power sources for robotics.

U.S. Pat. No. 5,807,011 involves a foot system for a walking robot. Thisdisclosure describes a cylindrical connection member disposed at acenter portion of the foot system for being connected to a leg system.It also describes a shock absorber supporting member and front and reartoes pivotally connected to an ankle member. Useful as particularrobotic foot design, this reference, however, does not involve the useof monopropellants as power sources as discussed and claimed herein.

European Patent Application EP 0859143 involves a single stagemonopropellant pressurization system wherein a monopropellant is storedwithin a tank. A gas generator supplied by the tank generates warm gasto pressurize other tanks. Disclosed monopropellants include hyrazine ormonomethyl hydrazine or a combination of these fuels and possibly otheradditives such as water. Similar to the other references mentionedabove, this reference does not disclose or suggest the technologydiscussed and claimed herein.

In summary, although conventional techniques may offer their ownsignificant advantages, they, however, suffer from shortcomings as well.In particular, conventional technology does not disclose or suggest howto fully take advantage of monopropellant power sources. Moreparticularly, conventional technology does not disclose or suggest howone could use monopropellant (or hypergolic bipropellant) sources offuel to drive robotic actuators so that a more efficient, effectiveuntethered mobile robot can be realized. The shortcomings ofconventional technology, however, are addressed by the techniquesdisclosed and claimed below.

SUMMARY OF THE INVENTION

Embodiments of the present invention overcome problems mentioned aboveby utilizing monopropellants or hypergolic bipropellants to powerrobotic actuators in an effective manner. In one embodiment, a systemutilizes a liquid monopropellant, such as hydrogen peroxide (H₂O₂) or aHAN (hydroxyl ammonium nitrate)-based fuel, as a gas generator used topower a pneumatic-type actuator. Such an embodiment may be implementedby storing the liquid monopropellant in a pressurized tank and releasingit through a control valve onto a catalyst, which causes a reaction thatgenerates gaseous products. The flow of pressurized gaseous products maythen be controlled through the use of proportional flow valves tocontrol the motion or force output of an actuator. Other embodiments aredescribed in the following section.

Unlike the combustion of hydrocarbon fuels, this approach does notrequire premixing, pre-compression, or an ignition system in order togenerate gaseous products. Additionally, the monopropellant approachenables flow control of the liquid state rather than the gaseous stateof the fuel, which greatly decreases energy loss from flow control, andgreatly simplifies the design of the flow control valve (i.e., itsignificantly decreases the flow rate passing through the valve). Theanalogous procedure cannot be accomplished electrically or with anyother conventional form of power control.

In one respect, the invention is a centralized monopropellant actuatorsystem that includes a blowdown fuel tank, a pressure reservoir, acentralized catalyst pack, a multi-chamber piston actuator, and two ormore valves. As used herein, the plural “valves” shall be interpretedbroadly to refer to any structure having more than one mechanism orpathway for regulating flow. As used in this disclosure, therefore,“valves” may properly describe (but would not be limited to) even asingle three or four-way valve. The blowdown fuel tank has a firstsection that is pre-pressurized with inert gas and a second section thatcontains a monopropellant. The pressure reservoir is coupled to thesecond section of the blowdown fuel tank. The centralized catalyst packis coupled to the second section of the blowdown fuel tank and isconfigured to release gaseous products into the pressure reservoir. Themulti-chamber piston actuator is coupled to the pressure reservoir. Thetwo or more valves are coupled to the actuator and are configured tocontrol the flow of the gaseous products into chambers of the actuatorto create controllable forces upon the piston.

In other respects, the monopropellant may be hydrogen peroxide. Themonopropellant may be hydroxyl ammonium nitrate. The inert gas may benitrogen. The system may also include one or more fuel valves coupled tothe blowdown fuel tank and pressure reservoir. Those one or more fuelvalves may be automatically controllable according to the pressure ofthe blowdown fuel tank and the pressure of the pressure reservoir. Thecentralized catalyst pack may include pellets coated or plated with acatalyzing agent. The centralized catalyst pack may be external to thepressure reservoir. The centralized catalyst pack, on the other hand,may be inside the pressure reservoir. The two or more valves of thesystem may include two inlet valves coupled to two inlet ports of theactuator and two exhaust valves coupled to two exhaust ports of theactuator.

In another respect, the invention is an untethered mobile robotincluding the centralized monopropellant actuator system describedabove. In yet another respect, the invention is a method for creatingcontrollable forces upon an actuator by using that centralizedmonopropellant actuator system.

The invention is also a distributed monopropellant actuator system thatincludes a blowdown fuel tank, a multi-chamber piston actuator, and twoor more distributed catalyst packs. The blowdown fuel tank has a firstsection that is pre-pressurized with inert gas and a second section thatcontains a monopropellant. The multi-chamber piston actuator is coupledto the blowdown fuel tank by two or more fuel valves. The two or moredistributed catalyst packs are coupled to the two or more fuel valvesand are configured to release gaseous products into chambers of theactuator to create controllable forces upon the piston.

In other respects, the distributed catalyst packs may be integrated intothe actuator. The distributed catalyst packs, on the other hand, may beexternal to the actuator. The system described above may also includetwo exhaust valves coupled to two exhaust ports of the actuator.

In another respect, the invention is an untethered mobile robotincluding the distributed monopropellant actuator system describedabove. In yet another respect, the invention is a method for creatingcontrollable forces upon an actuator comprising by using thatdistributed monopropellant actuator system.

In another respect, the invention is a centralized hypergolicbipropellant actuator system including a blowdown fuel tank, a blowdownoxidizer tank, a pressure reservoir, a multi-chamber piston actuator,and four or more valves. The blowdown fuel tank has a first section thatis pre-pressurized with inert gas and a second section that contains afuel. The blowdown-oxidizer tank has a first section that ispre-pressurized with inert gas and a second section that contains anoxidizer. The pressure reservoir is coupled to each blowdown tank and isconfigured to accept gaseous products from a controlled reaction of thefuel and oxidizer. The multi-chamber piston actuator is coupled to thepressure reservoir. The four or more valves are coupled to the actuatorand are configured to control the flow of the gaseous products intochambers of the actuator to create controllable forces upon the piston.

In other respects, the four or more valves may include four inlet valvescoupled to two inlet ports of the actuator and two exhaust valvescoupled to two exhaust ports of the actuator.

In another respect, the invention is an untethered mobile robotincluding the centralized hypergolic bipropellant actuator systemdescribed above. In yet another respect, the invention is a method forcreating controllable forces upon an actuator by using that centralizedhypergolic bipropellant actuator system.

In another respect, the invention is a distributed hypergolicbipropellant actuator system including a blowdown fuel tank, a blowdownoxidizer tank, and a multi-chamber piston actuator. The blowdown fueltank has a first section that is pre-pressurized with inert gas and asecond section that contains a fuel. The blowdown oxidizer tank has afirst section that is pre-pressurized with inert gas and a secondsection that contains an oxidizer. The multi-chamber piston actuator iscoupled to each blowdown tank by four or more fuel valves, and thevalves are configured to controllably mix and react the fuel andoxidizer to release gaseous products into chambers of the actuator tocreate controllable forces upon the piston.

In other respects, the system may also include two exhaust valvescoupled to two exhaust ports of the actuator.

In another respect, the invention is an untethered mobile robotcomprising the distributed hypergolic bipropellant actuator systemdescribed above. In yet another respect, the invention is a method forcreating controllable forces upon an actuator by using that distributedhypergolic bipropellant actuator system.

BRIEF DESCRIPTION OF THE DRAWINGS

The following drawings form part of the present specification and areincluded to further demonstrate certain aspects of the presentinvention. The invention may be better understood by reference to one ormore of these drawings in combination with the detailed description ofspecific embodiments presented herein. These drawings illustrate by wayof example and not limitation, and they use like references to indicatesimilar elements. The drawings include:

FIG. 1A is a schematic diagram of a centralized monopropellant poweredactuator embodiment. In the figure, the monopropellant is shown forpurposes of illustration powering a linear pneumatic cylinder-typeactuator. The concept is generalizable to any fluid-powered actuator,such as rotary vein-type actuators, etc.

FIG. 1B is a schematic diagram of a variant of FIG. 1A with a catalystpack external to the pressure tank. FIG. 1C is a detail of the catalystpack of FIG. 1 a.

FIG. 2A is a schematic diagram of a distributed monopropellant poweredactuator embodiment.

FIG. 2B is a schematic diagram of a variant of FIG. 2A with the catalystpacks integrated into the actuator housing.

FIGS. 2C and 2D are schematic diagrams showing details of the catalystarrangement in FIG. 2B.

FIG. 3 is a schematic diagram of a distributed hypergolic bipropellantpowered actuator embodiment.

FIG. 4 is a schematic diagram of a centralized hypergolic bipropellantpowered actuator embodiment.

DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

Embodiments described herein are applicable to a wide range of differentindustrial applications. Foremost, the monopropellants can be used topower robotic actuators. However, with the benefit of this disclosure,it will be apparent that this technology is applicable to many otherends. For instance, it may be used for any self-powered applicationrequiring a high energy and power density control actuator.

In one embodiment, an actuation system may provide direct chemical tomechanical energy conversion from an energy source that is approximatelyan order of magnitude more energy dense and power dense than the bestcommercially available lithium-thionyl-chloride orlithium-manganese-dioxide electrochemical batteries. This embodimentutilizes monopropellants such as, but not limited to, hydrogen peroxide(H₂O₂) or Hydroxyl Ammonium Nitrate (HAN) formulations to maintain ahigh-pressure pneumatic reservoir. This reservoir, in turn, may beutilized as a controllable power source for a system of pneumaticactuators.

First Embodiment (FIGS. 1A-1C)

FIG. 1A illustrates a centralized monopropellant actuator embodiment. Inthis embodiment, the chemical energy of a monopropellant is released andstored in a central location and used to drive one or morepneumatic-type actuators. To this end, a blowdown fuel tank 10 ispre-pressurized with nitrogen or other inert gas 11 such that amonopropellant 12 is maintained at a sufficiently high pressure asmeasured by the pressure gage 13. The flow of monopropellant through afuel line 14 is controlled by either a proportional or on/off liquidvalve 15. Being driven by the higher pressure of the fuel tank 10, themonopropellant flows through line 14, through valve 15 (if it is open orpartially open), and through line 16. Line 16 enters the pressurereservoir 17 where the monopropellant disassociates and expands intogaseous products within the catalyst pack 18. After disassociation, thegaseous products flow through the top of the screened surface of 18 intothe pressure reservoir 17. The control of valve 15 is dictated by anautomatic control law dependent upon pressure sensors 13 and 19 (asindicated by dashed line 20) such that a desired pressure is maintainedwithin the pressure reservoir 17.

Upon maintaining a desired high pressure within the pressure reservoir17, the gaseous products flow through line 21 and flow throughproportional valves 22 and 23 into the chambers of a pneumatic-typeactuator 26 via inlet ports 24 and 25. The pressure developed within thechambers of 26, due the flow of gaseous product through inlets 24 and25, create controllable forces on piston 28 resulting in the delivery ofcontrolled positive mechanical power and subsequent controlled force ormotion of plunger 27. Conversely, gaseous product can flow throughexhaust ports 29 and 30 in a proportional manner as governed byproportional valves 31 and 32 resulting in the controlled dissipation ofmechanical power via plunger 27. With the benefit of the presentdisclosure, those having skill in the art will recognize that the valvedesign may be modified to incorporate, for instance, three-way orfour-way valves. For instance, valves 22, 23, 31, and 32 may be achievedusing a four-way spool valve.

FIG. 1B shows a variant of FIG. 1A where the catalyst pack 18 isexternal to the pressure reservoir 17. Depending on the desiredconfiguration of the device, the variant shown in FIG. 1B may be moredesirable than the catalyst pack being integrated within the pressurereservoir as shown in FIG. 1A.

FIG. 1C shows details of the catalyst pack of FIG. 1A A line 114 (sameas line 16 in FIG. 1 a) delivers liquid monopropellant to the catalystpack. The monopropellant enters the catalyst pack through a screen 115(or other geometry transparent to the flow of liquid). The inside of thecatalyst pack 116 contain pellets (not shown), or other geometry, coatedor plated with a catalyzing agent. Being exposed to the catalyticsurface of the pellets, the liquid monopropellant disassociates into agaseous product and is allowed to escape the catalyst pack through ascreened surface 117. All other surfaces such as 118 and 119 are eithersolid or screened such that the catalyzing agent is contained within thecatalyst pack.

Second Embodiment (FIGS. 2A-2D)

FIG. 2A illustrates a distributed monopropellant actuator embodiment. Inthis embodiment, the chemical energy of a monopropellant is distributedto one or more pneumatic-type actuators and released in a controlledmanner inside the appropriate cylinder of the appropriate actuator.Shown in FIG. 2A is a blowdown fuel tank 33 pre-pressurized with aninert gas 34 and containing a monopropellant 35. This fuel tank 33 isinstrumented with a pressure sensor 36 such that the pressure of themonopropellant liquid can be monitored. The liquid monopropellant isdelivered via line or lines 37 to various pneumatic-type actuators (suchas 44). Proportional valves 38 or 39 control the flow of monopropellantsuch that it flows through a catalyst pack 40 and/or 41. The catalystpacks contain catalytic agents such that the monopropellant may flowinto, disassociate inside, and flow out of the pack without thecatalytic agent being allowed to escape. The gaseous products of themonopropellant produced inside the catalyst packs flows through inlets42 and 43 into the chambers of a pneumatic-type actuator 44. In asimilar manner as discussed in FIG. 1A of the first embodiment, thegaseous products are capable of delivering positive mechanical power, ordissipating negative mechanical power through piston 46 and plunger 45.Exhaust ports 47 and 48 and proportional valves 49 and 50 are similar tothose discussed in FIG. 1A. With the benefit of the present disclosure,those having skill in the art will recognize that the valve design maybe modified to incorporate, for instance, three-way or four-way valves.For instance, valves 38 and 39 may be achieved using a three-way valve.The same is true for valves 49 and 50.

FIG. 2B shows a variant for FIG. 2A where the catalyst packs 40 and 41are integrated into the pneumatic-type actuator. FIG. 2C shows a detailof the integrated catalyst pack (shown as 40 in FIG. 2B). The inlet line101 allows liquid monopropellant to enter the catalyst pack via a screen(or other geometry) 102. The inside of the catalyst pack 103 is filledwith pellets coated or plated with a catalytic agent (not shown).Surface 104 is screened or otherwise vented such that the gaseousproducts of the monopropellant are allowed to escape into the upperchamber of the pneumatic cylinder. This upper catalyst pack is ofannular shape such that the plunger (45 in FIG. 2A) is unobstructed bythe pack by passing through orifice 107. The contents of the upperchamber of the pneumatic-type actuator are allowed to exhaust throughopening 105 and flow through line 106 such that the exhaust does notpass through the catalytic agent (as it would impart an unwanted flowrestriction).

FIG. 2D shows a similar catalyst pack for the lower chamber of apneumatic-type actuator (for which there is no connecting plunger to thepiston). The inlet 108. The screened opening 109. The interior of thecatalyst pack 110 filled with pellets (not shown). The screened surfaceis 111. The exhaust opening is 112. The exhaust line is 113.

Third Embodiment (FIG. 3)

FIG. 3 illustrates a distributed hypergolic bipropellant poweredactuator embodiment. In this embodiment, a liquid (or gaseous) fuel anda liquid (or gaseous) oxidizer constituting a hypergolic bipropellantmixture are delivered to one or more pneumatic-type actuators. Thechemical energy of the fuel is released upon contact with the oxidizerlocally within each actuator. With regard to a liquid fuel and liquidoxidizer, FIG. 3 illustrates one possible configuration of thisembodiment. A blowdown fuel tank 51 is pre-pressurized with an inert gas52 such that the fuel 53 is under pressure and is monitored by pressuresensor 54. A similar blowdown tank 56 contains a pre-pressurized inertgas 57 such that the oxidizer 58 is under pressure and is monitored bypressure sensor 59. Fuel and oxidizer is transported to a pneumatic-typeactuator via lines 55 and 60 respectively. Proportional control valves61 and 62 control the flow of fuel while proportional control valves 63and 64 control the flow of oxidizer to each chamber of a pneumatic-typeactuator 67. Upon mixing and reacting in a controlled manner at inletports 65 and 66, the gaseous reaction products cause an increase ofpressure within either the upper or lower chamber of the actuator andconsequently deliver a controlled force to piston 69. This forcedelivers positive mechanical power to the environment via plunger 68. Inan analogous manner as described in the first and second embodiments,mechanical power is dissipated via exhaust posts 70 and 71 and thecontrol of proportional exhaust valves 72 and 73.

Fourth Embodiment (FIG. 4)

FIG. 4 illustrates a centralized hypergolic bipropellant poweredactuator embodiment. In this embodiment, a liquid (or gaseous) fuel anda liquid (or gaseous) oxidizer constituting a hypergolic bipropellantmixture are delivered to a centralized pressure reservoir. The chemicalenergy of the fuel is released upon contact with the oxidizer within thereservoir. The pressure within the reservoir is then used to drive oneor more pneumatic-type actuators. The fuel and oxidizer tanks aresimilar to those described in the third embodiment where 74, 75, 76, 77,79, 80, 81, and 82 are similar to 51, 52, 53, 54, 56, 57, 58, and 59 ofFIG. 3. Fuel and oxidizer flows through lines 78 and 83 respectively toproportional or on/off valves 84 and 85 respectively. Based on pressuresensors 77, 82 and 88, valves 84 and 85 are governed by a control lawsuch that a desired pressure in maintained within the pressure reservoir87. After passing through valves 84 and 85, fuel and oxidizer come incontact with one another and react to create a high pressure gaseousproduct within the pressure reservoir 86. The remaining portion of thesystem is similar to that described in the first embodiment where 89-100are analogous to 21-32.

Fifth Embodiment (Robotics)

As will be understood by those having skill in the art with the benefitof the present disclosure, any one of the systems described above (orany of the systems acting in combination) can be used as a power sourcefor a myriad of applications—including robotic applications. Inparticular, the systems may be used to power an untethered mobile robotso that shortcomings discussed in the background of this disclosure canbe avoided or eliminated.

Sixth Embodiment (Methods)

As will be understood by those having skill in the art with the benefitof the present disclosure, any one of the systems described above (orany of the systems acting in combination) can be operated as a generalmethod for controlling one or more actuators. These actuators may beinstalled in a myriad of different devices—including robotic devices asdescribed above. In particular, the systems may be used as a method topower an untethered mobile robot so that shortcomings discussed in thebackground of this disclosure can be avoided or eliminated.

While the present disclosure may be adaptable to various modificationsand alternative forms, specific embodiments have been shown by way ofexample and described herein. However, it should be understood that thepresent disclosure is not intended to be limited to the particular formsdisclosed. Rather, it is to cover all modifications, equivalents, andalternatives falling within the spirit and scope of the disclosure asdefined by the appended claims.

Moreover, the different aspects of the disclosed apparatus and methodsmay be utilized in various combinations and/or independently. Thus theinvention is not limited to only those combinations shown herein, butrather may include other combinations. Those of skill in the art willunderstand that numerous other modifications may be made to thedisclosed method and apparatus, but all such similar substitutes andmodifications are deemed to be within the spirit, scope and concept ofthe invention.

1. A centralized monopropellant actuator system, comprising: a blowdownfuel tank having a first section that is pre-pressurized with inert gasand a second section that contains a monopropellant; a pressurereservoir coupled to the second section of the blowdown fuel tank; acentralized catalyst pack coupled to the second section of the blowdownfuel tank and configured to release gaseous products into the pressurereservoir; a multi-chamber piston actuator coupled to the pressurereservoir; and two or more valves coupled to the actuator and configuredto control the flow of the gaseous products into chambers of theactuator to create controllable forces upon the piston.
 2. The system ofclaim 1, wherein the monopropellant comprises hydrogen peroxide.
 3. Thesystem of claim 1, wherein the monopropellant comprises hydroxylammonium nitrate.
 4. The system of claim 1, wherein the inert gascomprises nitrogen.
 5. The system of claim 1, further comprising one ormore fuel valves coupled to the blowdown fuel tank and pressurereservoir, the one or more fuel valves being automatically controllableaccording to the pressure of the blowdown fuel tank and the pressure ofthe pressure reservoir.
 6. The system of claim 1, wherein thecentralized catalyst pack comprises pellets coated or plated with acatalyzing agent.
 7. The system of claim 1, wherein the centralizedcatalyst pack is external to the pressure reservoir.
 8. The system ofclaim 1, wherein the centralized catalyst pack is inside the pressurereservoir.
 9. The system of claim 1, wherein the two or more valvescomprises two inlet valves coupled to two inlet ports of the actuatorand two exhaust valves coupled to two exhaust ports of the actuator. 10.An untethered mobile robot comprising the centralized monopropellantactuator system of claim
 1. 11. A method for creating controllableforces upon an actuator comprising use of the centralized monopropellantactuator system of claim
 1. 12. A distributed monopropellant actuatorsystem, comprising: a blowdown fuel tank having a first section that ispre-pressurized with inert gas and a second section that contains amonopropellant; a multi-chamber piston actuator coupled to the blowdownfuel tank by two or more fuel valves; and two or more distributedcatalyst packs coupled to the two or more fuel valves and configured torelease gaseous products into chambers of the actuator to createcontrollable forces upon the piston.
 13. The system of claim 12, whereinthe monopropellant comprises hydrogen peroxide.
 14. The system of claim12, wherein the monopropellant comprises hydroxyl ammonium nitrate. 15.The system of claim 12, wherein the inert gas comprises nitrogen. 16.The system of claim 12, wherein the distributed catalyst packs comprisepellets coated or plated with a catalyzing agent.
 17. The system ofclaim 12, wherein the distributed catalyst packs are integrated into theactuator.
 18. The system of claim 12, wherein the distributed catalystpacks are external to the actuator.
 19. The system of claim 12, furthercomprising two exhaust valves coupled to two exhaust ports of theactuator.
 20. An untethered mobile robot comprising the distributedmonopropellant actuator system of claim
 12. 21. A method for creatingcontrollable forces upon an actuator comprising use of the distributedmonopropellant actuator system of claim
 12. 22. A centralized hypergolicbipropellant actuator system, comprising: a blowdown fuel tank having afirst section that is pre-pressurized with inert gas and a secondsection that contains a fuel; a blowdown oxidizer tank having a firstsection that is pre-pressurized with inert gas and a second section thatcontains an oxidizer; a pressure reservoir coupled to each blowdown tankand configured to accept gaseous products from a controlled reaction ofthe fuel and oxidizer; a multi-chamber piston actuator coupled to thepressure reservoir; and four or more valves coupled to the actuator andconfigured to control the flow of the gaseous products into chambers ofthe actuator to create controllable forces upon the piston.
 23. Thesystem of claim 22, wherein the inert gas comprises nitrogen.
 24. Thesystem of claim 22, wherein the four or more valves comprises four inletvalves coupled to two inlet ports of the actuator and two exhaust valvescoupled to two exhaust ports of the actuator.
 25. An untethered mobilerobot comprising the centralized hypergolic bipropellant actuator systemof claim
 22. 26. A method for creating controllable forces upon anactuator comprising use of the centralized hypergolic bipropellantactuator system of claim
 22. 27. A distributed hypergolic bipropellantactuator system, comprising: a blowdown fuel tank having a first sectionthat is pre-pressurized with inert gas and a second section thatcontains a fuel; a blowdown oxidizer tank having a first section that ispre-pressurized with inert gas and a second section that contains anoxidizer; a multi-chamber piston actuator coupled to each blowdown tankby four or more fuel valves, the valves configured to controllably mixand react the fuel and oxidizer to release gaseous products intochambers of the actuator to create controllable forces upon the piston.28. The system of claim 27, wherein the inert gas comprises nitrogen.29. The system of claim 27, further comprising two exhaust valvescoupled to two exhaust ports of the actuator.
 30. An untethered mobilerobot comprising the distributed hypergolic bipropellant actuator systemof claim
 27. 31. A method for creating controllable forces upon anactuator comprising use of the distributed hypergolic bipropellantactuator system of claim 27.